Y12 assessment mark scheme

6732 Unit Test PHY2 June 2004 (electricity only)

1. Charge

Charge is the current x time ü ( Where you see this symbol there is supposed to be a tick) 1

Potential difference

Work done per unit charge [flowing] ü 1

Energy

9V x 20C ü

=180J ü 2

Total 4

2. Number of electrons

(-64 x 10^-9C)/(-1.6 x 10^-19 C) = 4.0 x 10¹¹ electrons

Use of n = Q/e ü

Seeing 1.6 x 10^-19 C ü

Answer of 4.0 x 10¹¹ (electrons) ü 3

[Use of a unit is a ue] [-ve answer: 2/3]

Rate of flow

(6.4 x 10-⁸ C)/3.8 s = 16.8/17 [uC s-¹] OR 16.8/17 x 10-⁹ [C s-¹]

(6.4) / 3.8 s i.e. use of I = Q / t [Ignore powers of 10] ü

Correct answer [No e.c.f] [1.7 or 1.68 x 10-⁸ or 1.6 x 10^-8 ü 2

Unit

Amp(ere)/A ü 1

Total 6

6 Explanation of observation

Any two from:

• LED on reverse bias/R in LED infinite/ LED wrong way round
• so current is zero /LED does not conduct / very small reverse bias current
• since V = IR.
• V=0x1K=0V üü

Explanation of dimness

Rv very large / R_v much greater than RLED

Current very low / pd across LED very small (not zero) üü 2

Circuit diagram

LED in forward bias ü

Variation of pd across LED ü

Voltmeter in parallel with LED alone ü 3

(LED in series with voltmeter 0/3]

total 7

7. Circuit diagram

Ammeter in series with cell and variable resistor (correct symbol) ü

Voltmeter in parallel with cell OR variable resistor ü 2

Power output at point X

Power = voltage x current ü

=0.45V x 0.6A

= 0.27 W ü 2

Description of power output

Any three from:

Current zero; power output zero/small/low

• As current increases power output also increases

• Then (after X ) power decreases

• Maximum current; power output zero ü ü ü 3

[Accept reverse order]

e.m.f. of cell

0.58 V ü 1

Internal resistance

Attempt to use " lost volts" OR E = V + IR current ü

_ 0.58V-0.45V 0.6 A

= 0.217 / 0.2 ohm ü 2

[ecf an emf greater than 0.45 V]

Total 10

8 Statement 1

Statement is false ü

Wires in series have same current ü

Use of I = nAev with n and e constant ü

[The latter two marks are independent] 3

Statement 2

Statement is true ü

Resistors in parallel have same p.d. ü

Use of Power = V²/R leading to R inc, power dec ü

OR as R inc I dec leading to a lower value of VI

3^rd mark consequent on second 3

total 6